1. Field of the Invention
The present invention relates to an acoustic monitoring device. More particularly, the acoustic monitoring device has a multiplexing circuit that records acoustic activity with the occurrence of a triggering event. Most particularly, the acoustic monitoring device may be used to detect, identify and assess damage within a solid medium.
2. Brief Description of the Related Art
Generally in acoustic emission (AE) monitoring, sensors remain active with each sensor having its own acquisition channel. As such, AE monitoring is extremely inefficient in monitoring acoustic emissions that occur at sporadic and random intervals and rates.
In a typical AE instrument, signals from each sensor are monitored by their own channel or data acquisition hardware, requiring the same number of channels of acquisition as acoustic sensors. In AE instruments which have fewer channels of data acquisition hardware than sensors, two approaches of switching sensors to data acquisition channels have been used. The first approach has been to assign certain sensors to be monitored. A manual or computer controlled switch is used to select which sensors are to be monitored. Unconnected sensors are not monitored during a given test, but can be connected for another test by disconnecting some of the previously monitored sensors. The second approach has been to switch sensors based on a clock or timing device. During a first period of time one group of sensors are connected to the data acquisition hardware and are actively monitored, while the remaining sensors are disconnected and ignored. At the end of this predefined first period of time, another group of sensors are connected by a switch and the original group disconnected. This method of data acquisition is widely used for monitoring a variety of sensor inputs such as temperature, pressure, strain, acceleration, ultrasonic sensors, etc.
The disadvantages of having one channel of data acquisition per sensor system are significant. These disadvantages include added weight, space, power, cost, etc. to an AE system. The acquisition hardware typically requires the most power and space, and is the heaviest part of an AE system. For aerospace applications, these additional weight and power requirements are unacceptable. Although conventional multiplexing reduces the number of data acquisition channels, a number of sensors are not actively monitored when they are disconnected from the data acquisition hardware. If a damage event occurs which generates an AE signal when the sensor is not being monitored, the damage event will not be detected.
Acoustic emission (AE) monitoring has been used for nondestructive evaluation in the petrochemical and power industries to monitor structures, such as pressure vessels. However, the use of large numbers of channels that are required for AE acquisition has limited AE monitoring for many applications. For example, AE monitoring for miles of piping in a typical petrochemical or nuclear power plant would require a large number of acoustic sensors. The complexity and expenses of the acoustic sensors and accompanying data acquisition hardware, per channel, restricts the ability to use AE monitoring. In other possible applications, such as structural monitoring for aircraft and spacecraft, the weight and power requirements for large numbers of data acquisition channels are limiting factors. In acoustic emission (AE) monitoring, a trade-off has existed between maximizing the number of AE sensors for accurate source location and signal detection, and the limitations (e.g., space, weight, cost, power, etc.) of the required instrumentation.
The present invention includes an acoustic monitoring device comprising the components of at least two acoustic sensors capable of sensing acoustic vibrations from a solid medium, a triggering mechanism responsive to a set parameter first occurring at one of the acoustic sensors, a multiplexing circuit connected to the triggering mechanism capable of receiving a triggering event and monitoring sensors adjacent to a triggered sensor, and at least one recording component responsive to the multiplexing circuit.
The present invention further includes a method for monitoring acoustic emissions comprising the steps of providing an acoustic monitoring device comprising the components of at least two acoustic sensors capable of sensing acoustic vibrations from a solid medium, a triggering mechanism responsive to a set parameter first occurring at one of the acoustic sensors, a multiplexing circuit connected to the triggering mechanism capable of receiving a triggering event and monitoring sensors adjacent to a triggered sensor, and at least one recording component responsive to the multiplexing circuit forming a connection between the acoustic monitoring device and the solid medium capable of detecting damage of the solid medium; and monitoring the sensors for a triggering event.
Additionally, the present invention includes an acoustic monitoring product made by the process comprising the steps of monitoring acoustic sensors for a triggering event within a solid medium and recording acoustical responses from at least one acoustic sensor after a triggering event occurs at an adjacent acoustic sensor.
The present invention is particularly applicable for detecting, locating and assessing damage to a solid medium, such as piping, aircraft, spacecraft, ships, buildings, and/or other similar structures, through the monitoring of acoustic vibrations within the solid medium.